The long term goals of this project are to gain a better understanding of the cellular and molecular mechanisms involved in the regulation of neuronal survival during development and the pathways by which neurons undergo programmed cell death (PCD). The specific studies proposed here arise from previous studies by us and others using avian embryo spinal motoneurons (MNs) as a model to examine the means by which trophic molecules and other cell-cell signals regulate survival and death both in vivo and in vitro. A unique aspect of the proposal is the use of both in vitro and in vivo models of PCD. The in vitro assay will allow us to distinguish direct vs indirect effects on MNs, whereas the in vivo model provides a means to evaluate the physiological significance of our in vitro observations. The specific aims of this proposal are designed to address several questions regarding MN survival and death. These are as follows: l) Are there specific muscle-derived (or other) trophic agents that act to promote MN survival in vitro and in vivo and can these agents, either alone or in combination, rescue all of the MNs that undergo naturally occurring PCD? 2) Does the inhibition of endogenous sources of these putative factors by neutralizing antibodies or anti- sense methods reduce MN survival? 3) Are there specific known or novel genes and proteins that act to prevent (e.g. bcl-2) or induce (e.g ICE) the death of developing MNs? 4) Do postmitotic MNs that undergo PCD exhibit an abortive attempt to reenter the cell cycle and is this an important pathway that ultimately results in their subsequent degeneration? 5) Is the PCD of MNS associated with oxidative stress and is this an essential physiological pathway in the degradative events involved in their degeneration? These studies will help to clarify the role of specific neurotrophic agents in regulating motoneuron survival and will begin to address the issue of the role of specific genes and molecular pathways in the survival and death of developing neurons. it is also expected that these studies will result in a better understanding of the mechanisms involved in cell death during pathology and disease.